An LED screen has been widely used. In some special occasions, however, the LED screen is required to have a hollow structure, which is advantageous for: (1) not obstructing vision, so that objects in front of and behind the LED screen are visible; (2) a certain permeability of light, to meet indoor light requirements for a glass curtain wall or shop window employing the LED screens; (3) a mostly reduced impact on the overall decoration design in the scenario employing the LED screens; and (4) a certain artistic effect, especially in the case of a stage performance, to achieve a fancy effect that the displayed image is visible but the screen is invisible. Due to the above advantages, the hollow LED screen is particularly popular in some special scenarios such as airports, hotels, buildings with glass curtain wall, exhibition centers, performance stages and shop windows, and has an application effect much better than the conventional box-type LED screen. Both permeability of light and a pixel resolution are considered in designing the hollow LED screen, and under the same design conditions, the higher pixel resolution means the lower aperture ratio, which results in the worse permeability of light. Typical relations between pixel pitches and the corresponding pixel resolutions of the LED screen are listed in a table below:
pixel pitch (P)pixel resolution (R)40 mm 625 pixels/m225 mm 1600 pixels/m220 mm 2500 pixels/m216 mm 3906 pixels/m210 mm10000 pixels/m2 8 mm15625 pixels/m2 7 mm20408 pixels/m2 6 mm27777 pixels/m2 5 mm40000 pixels/m2* Note:the pixel resolution R is calculated by a formula: R = (1000 mm × 1000 mm)/(P × P).
It can be seen from the above table and formula that the pixel resolution increases in a geometric progression as the pixel pitch decreases. Obviously, if the pixel pitch is below 10 mm, the pixel resolution increases considerably even if the pixel pitch is reduced by merely 1 mm.
In the existing hollow LED screen, soldering pads of the display unit are disposed on an upper surface of a circuit board, so that LED lights welded on the soldering pads are located on the upper surface of the circuit board, thus the LED lights block light, and such structure reduces the permeability of light through the LED screen. Therefore, a high permeability of light cannot be ensured in the case of a high pixel resolution in the LED screen in the prior art.